Over the last few years, the use of digital cameras has increased enormously, with digital cameras now commonly being incorporated into other portable electronic equipment, particularly mobile telephones. Over the same period, the resolution of those digital cameras has also increased considerably, with mobile telephones now having 2 Megapixel cameras integrated into them and digital cameras with upwards of 6 million effective pixels being widely available. Digital cameras allow users to take large numbers of photographs, knowing that they can be selective about which and how many images they may subsequently choose to print and/or keep. This results in a large number of images files being created and stored on a digital camera, where the file size for each image may be large. Digital cameras are therefore commonly designed to accept removable media, such as an SD card or compact flash card, into a slot in the camera, with most, if not all, of the image files being stored on this removable media.
SenseCam is a wearable camera developed by Microsoft Research, one use of which is to assist with memory recall by enabling a user to rewind through the recent events experienced by the wearer of the device. This may be particularly useful for memory-impaired individuals, or where an individual has experienced a traumatic event (e.g. an elderly person's fall resulting in injury).
The device can capture very large numbers of images and in addition to capturing images, the device also records sensor data, such as movement, light level and temperature every second. This sensor data is used to trigger the capturing of images, for example, when there is a change in light level or sudden movement. A change in light level may indicate that a user has moved from one room to another, or from inside to outside and therefore the image captured will indicate a change in location (and environment) of the wearer. The device has a wide angle or fish-eye lens so that the user does not need to worry about pointing the device in a particular direction. An accelerometer is used for image stabilisation. In the current SenseCam prototypes the image data and the sensor data are stored in FLASH memory.
Having taken large numbers of digital photographs on a digital camera, in order to manipulate, print or distribute the images, the user needs to transfer (or upload) the data to a computer (or similar device). This is typically done either by removing the removable memory card from the camera and inserting this into a card reader connected to or integrated into a computer, or by physically connecting the camera to the computer using a lead, such as a USB or FireWire lead. Such ‘wired’ technologies provide a fast link between the camera and the computer (e.g. data rates of up to 480 Mb/s for USB 2.0 and 800 Mb/s for FireWire).
However, as wireless capability is integrated into digital cameras or digital cameras are integrated into wireless capable devices, such as mobile telephones, the uploading of images may be done over the wireless links. This may be particularly beneficial when the user is away from home and wishes to upload images to a web site or email them to a friend or colleague. However, this can be a slow and frustrating process because the data rates obtainable over the wireless connections are one or more orders of magnitude less than can be achieved through the wired connections. At the fast end of wireless connections is WiFi technology with IEEE 802.11a and 802.11g providing 54 Mb/s, however Bluetooth provides only 720 kb/s and realistic data rates over GPRS may only be 30-70 kb/s, particularly in busy cells. In addition to the lengthy download times caused by the slow data rates, the wireless transmission can use a lot of battery power, so that the device needs recharging frequently. The battery consumption is affected by both the distance between the device (the transmitter) and the receiver and the data rate. Of the wireless technologies listed above, GPRS transmission will drain a battery quickest, whilst Bluetooth will have the lowest battery consumption. Furthermore, transferring files may also be expensive, with wireless hotspot operators typically charging £6-£12 per hour (for WiFi) and mobile phone operators typically charging between £1 and £4 per Megabyte (for GPRS).